108 



HISTORY OF THE VEGETABLE KINaOOM. 



mode of gei-mination. In the dicotyledonous 

 embryo, the radicle is generally conical and pro- 

 tuberant; the caulicle is cylindrical; and the 

 gommnle is naked and concealed between the 

 bases of the two cotyledons, which are placed 

 face to face, and are directly applied upon each 

 other. Thus, in the kidney bean, the entire 

 uiass of the seed becomes first impregnated with 



<i, the radicle; b, tlie g^emmule; c c, the cotyledons; d, the 

 caulicle. 



humidity and swells. The episperm becomes 

 torn in an in-egular manner. I'resentl}', the 

 radicle, which formed a small conical prominence, 

 begins to elongate, peneti'ates into the ground, 

 and gives rise to small lateral ramifications of 

 extreme delicacy. Soon after, the gemmule, 

 which, until now, has remained concealed be- 

 tween the two cotyledons, rises upwards, and be- 

 comes apparent at the exterior. The caulicle 

 elongates, and raises the cotyledons out of the 

 ground, while the radicle proceeds farther into 

 it and ramifies there. The two cotyledons then 

 separate, and the gemmule is entirely free and 

 uncovered ; the leaflets of which it is composed 

 spread out, enlarge, become green, aud ah-eady 

 begin to extract from the atmosphere a portion 

 of the fluids which are to be employed in effect- 

 ing the growth of the young plant. Germina- 

 tion is now ended, and the second period of the 

 life of the plant commences. 



Some dicotyledonous plants have a peculiar 

 mode of germination. Thus, for example, we 

 very often find embryos that have alreadj^ ger- 

 minated, in the interior of certain fruits, which 

 are entirely closed all round. This is not un- 

 frequently seen in the fmits of the lemon tree, 

 in which it is not rare to f/nd several seeds al- 

 ready in a germinating stale. In the mangi'ove 

 tree which inhabits salt marshes, and shores of 

 the sea in the equinoxial regions, the embryo 

 begins to be developed, while the seed is still 

 contained in the pericarp. The radicle presses 

 against the pericarp, which it wears, and at 

 length perforates, and elongates at the outside, 

 sometimes more than a foot. The embryo then 



becomes detached, and, leaving the cotyledon.iTy 

 body in the seed, falls off, the radicle first, sinlcs 

 into the mud, and there continues to grow. In 

 the horse-chestnut, the common chestnut, and 

 some other dicotyledonous plants, the two coty- 

 ledons, which are very large and thicJc, are, in 

 most cases, directly united. In these, the radicle, 

 as it sinks into the ground, elongates the base 

 of the two cotyledons, and thus disengages the 

 gemmule, which shows itself above ground ; but 

 the two cotyledons are not raised by the gem- 

 mule, they remain below. 



Monocotyledonous embryos generally undergo 

 fewer changes, during germination, than those 

 of dicotyledonous plants; which is caused by 

 the uniformity of their internal structure. As 

 in the dicotyledones, the radicular extremity is 

 that which is first developed. It elongates, and 

 its coleorhiza bursts to allow a passage to the 

 radicular tubercle, which enlarges, and passes 

 dovvTiwards into the ground. Several smaller 

 roots usually spring from the lateral and inferior 

 parts of the caulicle. When they have acquired 

 a certain development, the principal radicle is 

 destroyed, and disappears. Accordingly, mono- 

 cotyledonous plants never have a tapering root 

 like the dicotyledonous. 



The cotyledon which contains the gemmule, 

 always enlarges more or less before it is perfor- 

 ated by that organ, which generally issues at the 

 lateral part of the cotyledon, scarcely ever at 

 the summit. When the gemmule has perforated 

 the cotyledon, the latter changes into a kind of 

 sheath which embraces the gemmule at its base. 

 It is to this sheath that the name of coleoptile 

 has been given. Cut 69. fig. a h, represents the 

 69. germination of a grain of com- 



mon wheat ; c c are the radi- 

 cles ; d d the gemmules, with 

 their sheath. It has already 

 beenremarked that, in whatever 

 position the seed is placed in 

 the soil, the gemmule invari- 

 ably ascends, and the radicle 

 descends. This is a beautiful 

 provision of nature; for had 

 this aiTangement not existed, 

 one half of the seeds of gxain sown, would have, in 

 all probabilitj-, been unproductive ; as the chances 

 are almost equal, that the end containing the 

 embryo falls either upwards or downwards. 



It now remains to consider the chemical changes 

 which take place in the seed, during the pro- 

 cess of germination, and regarding this a variety 

 of opinions have been advanced. The matter 

 contained in the cotyledons of seeds is not, in the 

 first instance, adapted for the nourishment of 

 the future germ ; before it can become so, it must 

 undergo certain changes in its chemical composi- 

 tion. It has been already shown that a seed is 

 no sooner placed in the ground than it begins to 



